This invention relates to a new type of solid particulate metallocene catalyst system useful for the polymerization and/or copolymerization of olefins. The invention is also related to a process for conducting polymerization of olefins using the inventive solid metallocene catalyst system.
The term xe2x80x9cMetallocenexe2x80x9d as used herein refers to a derivative of cyclopentadienylidene which is a metal derivative containing at least one cyclopentadienyl component which is bonded to a transition metal. The transition metal is selected from Groups IVB, VB, and VIB, preferably IVB and VIB. Examples include titanium, zirconium, hafnium, chromium, and vanadium. A number of metallocenes have been found to be useful for the polymerization of olefins. Generally, the more preferred catalysts are metallocenes of Zr, Hf, or Ti.
Generally, in order to obtain the highest activity from metallocene catalysts, it has been necessary to use them with an organoaluminoxane cocatalyst, such as methylaluminoxane. This resulting catalyst system is generally referred to as a homogenous catalyst system since at least part of the metallocene or the organoaluminoxane is in solution in the polymerization media. These homogenous catalysts systems have the disadvantage that when they are used under slurry polymerization conditions, they produce polymer which sticks to reactor walls during the polymerization process and/or polymer having small particle size and low bulk density which limits the commercial utility.
Some attempts to overcome the disadvantages of the homogenous metallocene catalyst systems are disclosed in U.S. Pat. Nos. 5,240,894, 4,871,705; and 5,106,804. Typically, these procedures have involved the prepolymerization of the metallocene aluminoxane catalyst system either in the presence of or in the absence of a support. An evaluation of these techniques has revealed that there is still room for improvement, particularly when the catalyst is one which is to be used in a slurry type polymerization where the object is to produce a slurry of insoluble particles of the end product polymer rather than a solution of polymer which could result in fouling of the reactor. In the operation of a slurry polymerization in a continuous loop reactor it is extremely important for efficient operations to limit polymer fouling of the internal surfaces of the reactor. The term xe2x80x9cfoulingxe2x80x9d as used herein refers to polymer buildup on the surfaces inside the reactor.
An improved type of solid metallocene catalyst composition that can be used in a slurry polymerization process was revealed in U.S. Pat. No. 5,498,581, the disclosure of which is incorporated herein by reference. That catalyst composition was prepared by combining a cocatalyst with a metallocene that had an olefinically unsaturated substituent, subjecting that mixture to prepolymerization with an olefin in the presence of a liquid to produce a solid prepolymerized catalyst, and separating the resulting prepolymerized catalyst from the liquid and the components dissolved in the liquid. Some specific variations of producing such catalysts are disclosed in WO 99/29738 and WO 98/52686, the disclosures of which are also incorporated herein by reference.
An object of the present invention is to provide yet further improvements for the making of solid catalyst systems of the type disclosed in U.S. Pat. No. 5,498,581. In accordance with another aspect of the present invention, there is provided a method for polymerizing olefins using the new improved version of such solid prepolymerized metallocene catalyst systems.
In accordance with the present invention, a solid particulate metallocene-containing catalyst system is produced by (a) combining an organoaluminoxane and at least one metallocene having at least one olefinic unsaturated substituent in an aliphatic liquid to form a liquid catalyst system, (b) conducting prepolymerization of at least one olefin in the presence of said liquid catalyst system, optionally in multiple steps, to produce a prepolymerized solid catalyst, and (c) separating the resulting solid from the liquid and the components dissolved in the liquid, said solid being the solid particulate metallocene catalyst system. The phrase xe2x80x9cliquid catalyst systemxe2x80x9d as used herein refers to the combination of the aluminoxane, the metallocene, and the aliphatic liquid, irrespective of whether the aluminoxane and/or the metallocene are dissolved in the liquid.
In accordance with another aspect of the present invention, the resulting inventive solid particulate metallocene-containing catalyst system is employed in the polymerization of an olefin by contacting the olefin with the inventive solid particulate metallocene-containing catalyst system under suitable reaction conditions.
A wide range of metallocenes are considered to be applicable to the present process. The essential feature is that the metallocene be one wherein at least one cyclopentadienyl-type ligand has a substituent having a polymerizable olefinic group. Some examples of such olefin-containing metallocenes are disclosed in U.S. Pat. No. 5,169,818 and published European Application No. 574,370. The invention is considered applicable to both bridged and unbridged metallocenes. The unbridged metallocenes can even include bridged ligands which contain two cyclopentadienyl-type radicals connected by a suitable bridging structure but wherein only one of the cyclopentadienyl-type radicals of that ligand is bonded to the transition metal. Alternatively the olefinic substituent can be on the bridge connecting the two cyclopentadienyl-type groups.
The metallocenes of the type contemplated as useful for the present invention include those represented by the formula Rx(Z)(Z)MQk wherein each Z bound to M and is the same or different and is a cyclopentadienyl-type ligand selected from substituted or unsubstituted cyclopentadienyl, indenyl, tetrahydroindenyl, octahydrofluorenyl, and fluorenyl ligands; R is a structural bridge linking the Z""s and M is a metal selected from the group consisting of IVB, VB, and VIB metals of the periodic table, each Q is the same or different and is selected from the group consisting of hydrogen, halogens, and organoradicals; x is 1 or 0; k is a number sufficient to fill out the remaining balances of M; further characterized by the fact that at least one Z has at least one olefinically unsaturated substituent attached. In bridged metallocenes this olefinically unsaturated substituent can be a branch on the bridging unit or on one or both of the cyclopentadienyl-type groups of the bridged ligands.
When a Q is an organo radical it can be selected from any of the organo radicals known to be suitable for metallocenes that are useful as polymerization catalysts. Some examples include aryl, alkyl, alkenyl, alkylaryl, and arylalkyl radicals. Preferably, if Q is an argano radical, the organo radical has 1 to 20 carbon atoms.
A particularly preferred type of bridged metallocene includes those in which the olefinically unsaturated substituent has the formula 
wherein Rxe2x80x3 is a hydrocarbyl diradical having 1 to 20 carbon atoms; more preferably 2 to 10; n is 1 or 0, and each Rxe2x80x2 is individually selected from the group consisting of organo radicals having 1 to 10 carbon atoms and hydrogen. Most preferably Rxe2x80x3 has at least two carbons in its main alkylene chain, i.e. it is a divalent ethylene radical or a higher homolog thereof.
Some olefinic branched bridged ligands useful for making metallocenes suitable for the present invention can be prepared by reacting a dihalo olefinic compound with an alkali metal salt of a suitable cyclopentadiene-type compound to produce a compound of the formula Zxe2x80x94Rxe2x80x94Z where R is a bridge having olefinic unsaturation and wherein each Z is the same or alternatively to first produce a compound of the formula Zxe2x80x94Rxe2x80x94X wherein X is a halogen and then reacting that compound with an alkali metal salt of another different cyclopentadiene-type compound to produce a compound of the formula Zxe2x80x94Rxe2x80x94Z wherein the two Z""s differ. Such reactions can be carried out using conditions of the type disclosed in U.S. Pat. No. 5,191,132.
An alternate technique for forming an olefinic branched bridged ligand involves reacting a carbonyl compound having olefinic unsaturation with a cyclopentadiene-type compound in the presence of a base and methanol to yield an alkenyl fulvene which is then reacted with an alkali metal salt of a cyclopentadiene-type compound, such as, for example, fluorene, to yield the unsaturated-branched-bridged ligand containing two cyclopentadienyl-type groups, i.e. fluorenyl and cyclopentadienyl. For example, one could react 5-hexene-2-one with cyclopentadiene using a procedure like that disclosed by Stone et al in J. Org. Chem. 49, 1849(1984) to yield 6-(but-3-enyl)-6-methylfulvene which could then be reacted with fluorenyllithium and subsequently hydrolyzed to yield 5-cyclopentadienyl-5-(9-fluorenyl)-1-hexene, also sometimes referred to as 1-(9-fluorenyl)-1-(cyclopentadienyl)-1-(methyl)-1-(but-3-enyl) methane.
The present invention thus envisions using bridged metallocenes prepared from vinyl terminated branched bridged ligands of the formula 
wherein n is a number typically in the range of about 0 to 20; more preferably 2-10; Riv is Si, Ge, C, or Sn; Rxe2x80x2xe2x80x3 and Rxe2x80x2 are each individually selected from hydrogen, or organo groups having 1 to 10 carbons. Currently preferred Rxe2x80x2 and Rxe2x80x2xe2x80x3 components are hydrogen or alkyl groups typically having 1 to 10 carbon atoms, or aryl groups typically having 6 to 10 carbon atoms. Z is a cyclopentadienyl-type radical as described earlier.
The metallocenes of such olefinically unsaturated branched-bridged ligands can be prepared by reacting the olefinically branched-bridged bis(cyclopentadienyl-type) ligand with an alkali metal alkyl to produce a divalent ligand salt that is then reacted with the transition metal compound to yield the metallocene, using the techniques generally known in the art for forming such metallocenes. See, for example, the technique disclosed in European Published Application 524,624, the disclosure of which is incorporated herein by reference.
Some typical examples of some metallocenes containing a substituent having olefinic unsaturation include 5-(cyclopentadienyl)-5-(9-fluorenyl)-1-hexene zirconium dichloride, bis(9-fluorenyl)(methyl)(vinyl)silane zirconium dichloride, bis(9-fluorenyl)(methyl)(prop-2-enyl)silane zirconium dichloride, bis(9-fluorenyl) (methyl)(but-3-enyl)silane zirconium dichloride, bis(9-fluorenyl)(methyl) (hex-5-enyl) silane zirconium dichloride, bis(9-fluorenyl)(methyl) (oct-7-enyl)silane zirconium dichloride, (cyclopentadienyl)(1-allylindenyl) zirconium dichloride, bis(1-allylindenyl) zirconium dichloride, (9-(prop-2-enyl) fluorenyl) (cyclopentadienyl) zirconium dichloride, (9-(prop-2-enyl) fluorenyl)(pentamethylcyclopentadienyl) zirconium dichloride, bis(9-(prop-2-enyl)fluorenyl) zirconium dichloride, (9-(cyclopent-2-enyl) fluorenyl) (cyclopentadienyl) zirconium dichloride, bis(9-(cyclopent-2-enyl) (fluorenyl) zirconium dichloride, 5-(2-methylcyclopentadienyl)-5-(9-fluorenyl)-1-hexene zirconium dichloride, 5-(fluorenyl)-5-(cyclopentadienyl)-1-hexene hafnium dichloride, (9-fluorenyl)(1-allylindenyl)dimethylsilane zirconium dichloride, 1-(2,7-di(alpha-methylvinyl)(9-fluorenyl))-1-(cyclopentadienyl)-1,1-dimethylmethane zirconium dichloride, 1-(2,7-di(cyclohex-1-enyl)(9-fluorenyl))-1-(cyclopentadienyl)-1,1-methane zirconium dichloride, 5-(cyclopentadienyl)-5-(9-fluorenyl)-1-hexene titanium dichloride, and the like.
These various metallocenes can be prepared by reacting the necessary cyclopentadienyl-type alkali metal salt with a transition metal compound. Some examples of such reactions are disclosed in the aforementioned published EPC application no. 524,624.
The organo aluminoxane component used in preparing the inventive solid catalyst system is an oligomeric aluminum compound having repeating units of the formula 
Some examples are often represented by the general formula (Rxe2x80x94Alxe2x80x94O)n or R(Rxe2x80x94Alxe2x80x94Oxe2x80x94)nAlR2. In the general alumoxane formula R is a C1-C5 alkyl radical, for example, methyl, ethyl, propyl, butyl or pentyl and xe2x80x9cnxe2x80x9d is an integer from 1 to about 50. Most preferably, R is methyl and xe2x80x9cnxe2x80x9d is at least 4. Aluminoxanes can be prepared by various procedures known in the art. For example, an aluminum alkyl may be treated with water dissolved in an inert organic solvent, or it may be contacted with a hydrated salt, such as hydrated copper sulfate suspended in an inert organic solvent, to yield an aluminoxane. Generally the reaction of an aluminum alkyl with a limited amount of water is postulated to yield a mixture of the linear and cyclic species of the aluminoxane.
In the first step of the present invention, the metallocene and aluminoxane are combined with an aliphatic liquid to form a liquid catalyst system. Examples of what is meant by aliphatic liquid include pentane, isopentane, hexane, octane, heptane, and the like. The amount of aliphatic liquid employed should preferably be such as to allow for good mixing in the subsequent steps and to allow for a desirable viscosity during the prepolymerization step.
It is preferred that the liquid catalyst system be prepared using an aluminoxane that is dissolved in an aromatic liquid. Examples of what is meant by aromatic liquid include benzene, toluene, ethylbenzene, diethylbenzene, and the like. The currently preferred aromatic liquid toluene. The amount of liquid in which the aluminoxane is dissolved is not particularly critical, however the aromatic liquid is commonly used in such an amount that the aluminoxane solution would contain about 5 to about 40 weight percent aluminoxane, more preferably about 10 to about 30 weight percent.
The amount of aliphatic liquid employed in step (a) can vary over a wide range depending upon the results desired. Typically, however, the aliphatic liquid would be used in such an amount that the volume ratio of the aliphatic liquid to the aromatic solution of aluminoxane would be in the range of from about 0.5/1 to about 15/1, more preferably about 1/1 to about 13.5/1, still more preferably at least 5/1, and even still more preferably at least 6/1.
In combining the metallocene and the aluminoxane the temperature is preferably kept below that which would cause the metallocene to decompose. Typically the temperature would be in the range of xe2x88x9250xc2x0 C. to 100xc2x0 C. Preferably, the metallocene, the aluminoxane, and the liquid diluent are combined at room temperature, i.e. around 10 to 30xc2x0 C. The reaction between the aluminoxane and the metallocene is relatively rapid. The reaction rate can vary depending upon the ligands of the metallocene. It is generally desired that they be contacted for at least about a minute to about 1 hour.
It is within the scope of the invention to form the liquid catalyst system in the presence of a particulate solid. Any number of particulate solids can be employed as the particulate solid. Typically the particulate solid can be any organic or inorganic solid that does not interfere with the desired end result. Examples include porous supports such as talc, inorganic oxides, and resinous support materials such as particulate polyolefins. Examples of inorganic oxide materials include oxides of metals of Groups II, III, IV or V of the Periodic Table, such as silica, alumina, silica-alumina, and mixtures thereof. Other examples of inorganic oxides are magnesia, titania, zirconia, and the like. Other suitable support materials which can be employed include such as, magnesium dichloride, and finely divided polyolefins, such as polyethylene. It is within the scope of the present invention to use a mixture of one or more of the particulate solids.
It is generally desirable for the solid to be thoroughly dehydrated prior to use, preferably it is dehydrated so as to contain less than 1% loss on ignition. Thermal dehydration treatment may be carried out in vacuum or while purging with a dry inert gas such as nitrogen at a temperature of about 20xc2x0 C. to about 1000C, and preferably, from about 300xc2x0 C. to about 800xc2x0 C. Pressure considerations are not critical. The duration of thermal treatment can be from about 1 to about 24 hours. However, shorter or longer times can be employed provided equilibrium is established with the surface hydroxyl groups.
Dehydration can also be accomplished by subjecting the solid to a chemical treatment in order to remove water and reduce the concentration of surface hydroxyl groups. Chemical treatment is generally capable of converting all water and hydroxyl groups in the oxide surface to relatively inert species. Useful chemical agents are for example, trimethylaluminum, ethyl magnesium chloride, chlorosilanes such as SiCl4, disilazane, trimethylchlorosilane, dimethylaminotrimethylsilane and the like.
The chemical dehydration can be accomplished by slurrying the inorganic particulate material such as, for example silica, in an inert low boiling hydrocarbon, such as for example, hexane. During the chemical dehydration treatment, the silica should be maintained in a moisture and oxygen free atmosphere. To the silica slurry is then added a low boiling inert hydrocarbon solution of the chemical dehydrating agent, such as, for example dichloroldimethylsilane. The solution is added slowly to the slurry. The temperature ranges during chemical dehydration reaction can be from about 20xc2x0 C. to about 120xc2x0 C., however, higher and lower temperatures can be employed. Preferably, the temperature will be about 50xc2x0 C. to about 100xc2x0 C. The chemical dehydration procedure should be allowed to proceed until all the substantially reactive groups are removed from the particulate support material as indicated by cessation of gas evolution. Normally, the chemical dehydration reaction will be allowed to proceed from about 30 minutes to about 16 hours, preferably, 1 to 5 hours. Upon completion of the chemical dehydration, the solid particulate material may be filtered under a nitrogen atmosphere and washed one or more times with a dry, oxygen free inert solvent. The wash solvents as well as the diluents employed to form the slurry and the solution of chemical dehydrating agent, can be any suitable inert hydrocarbon. Illustrative of such hydrocarbons are pentane, heptane, hexane, toluene, isopentane and the like.
Another chemical treatment that can be used on solid inorganic oxides such as silica involves reduction by contacting the solid with carbon monoxide at an elevated temperature sufficient to convert substantially all the water and hydroxyl groups to relatively inactive species.
The specific particle size of the support or inorganic oxide, surface area, pore volume, and number of hydroxyl groups is not considered critical to its utility in the practice of this invention. However, such characteristics often determine the amount of support to be employed in preparing the catalyst compositions, as well as affecting the particle morphology of polymers formed. The characteristics of the carrier or support must therefore be taken into consideration in choosing the same for use in the particular invention.
It is also within the scope of the present invention to add such a particulate solid to the liquid catalyst system after it has been formed and to carry out the prepolymerization in the presence of that solid.
The amount of aluminoxane and metallocene used in forming the liquid catalyst system for the prepolymerization can vary over a wide range.
Typically, however, the molar ratio of aluminum in the aluminoxane to transition metal of the metallocene is in the range of about 1:1 to about 20,000:1, more preferably, a molar ratio of about 50:1 to about 2000:1 is used. If a particulate solid, i.e. silica, is used generally it is used in an amount such that the weight ratio of the metallocene to the particulate solid is in the range of about 0.00001/1 to 1/1, more preferably 0.0005/1 to 0.2/1.
In a particularly preferred process the aromatic solution of the aluminoxane is combined with the metallocene before being combined with the aliphatic liquid. In another preferred process, however, the aromatic solution of the aluminoxane is combined with the aliphatic liquid and then combined with the metallocene. It is also within the scope of the present invention to combine the metallocene with the aliphatic liquid and then combine that mixture with the aromatic solution of the aluminoxane.
The prepolymerization is conducted in the liquid catalyst system, which can be a solution, a slurry, or a gel in a liquid. A wide range of olefins can be used for the prepolymerization. Typically, the prepolymerization will be conducted using an olefin, preferably selected from ethylene and non-aromatic alpha-olefins, and as propylene. It is within the scope of the invention to use a mixture of olefins, for example, ethylene and a higher alpha olefin can be used for the prepolymerization. The use of, a higher alpha olefin, such as 1-butene, with ethylene is believed to increase the amount of copolymerization occurring between the olefin monomer and the olefinically unsaturated portion of the metallocene.
The prepolymerization can be conducted under relatively mild conditions. Typically, this would involve using low pressures of the olefin and relatively low temperatures designed to prevent site decomposition resulting from high concentrations of localized heat. The prepolymerization typically occurs at temperatures in the range of about xe2x88x9215xc2x0 C. to about +110xc2x0 C., more preferably in the range of about +10 to about +30xc2x0 C. The amount of prepolymer can be varied but typically would be in the range of from about 1 to about 95 wt % of the resulting prepolymerized solid catalyst system, more preferably about 5 to 80 wt %. It is generally desirable to carry out the prepolymerization to at least a point where substantially all of the metallocene is in the solid rather than in the liquid since that maximizes the use of the metallocene.
After the prepolymerization, the resulting solid prepolymerized catalyst is separated from the liquid of the reaction mixture. Various techniques known in the art can be used for carrying out this step. For example, the material could be separated by filtration, decantation, or by vacuum evaporation. It is currently preferred, however, not to rely upon vacuum evaporation since it is considered desirable to remove substantially all of the soluble components in the liquid reaction product of the prepolymerization from the resulting solid prepolymerized catalyst before it is stored or used for subsequent polymerization. After separating the solid from the liquid, the resulting solid is preferably washed with a hydrocarbon and then dried using high vacuum to remove substantially all the liquids and other volatile components that might still be associated with the solid. The vacuum drying is preferably carried out under relatively mild conditions, i.e. temperatures below 100xc2x0 C. More typically the prepolymerized solid is dried by subjection to a high vacuum at a temperature of about 30xc2x0 C. until a substantially constant weight is achieved. A preferred technique employs at least one initial wash with an aromatic hydrocarbon, such as toluene, followed by a wash with a paraffinic hydrocarbon, such as hexane, and then vacuum drying.
It is within the scope of the present invention to contact the prepolymerization reaction mixture product with a liquid in which the prepolymer is sparingly soluble, i.e. a counter solvent for the prepolymer, to help cause soluble prepolymer to precipitate from the solution. Such a liquid is also useful for the subsequent washing of the prepolymerized solid.
It is also within the scope of the present invention to add a particulate solid of the type aforementioned after the prepolymerization. Thus one can add the solid to the liquid prepolymerization product before the counter solvent is added. In this manner soluble prepolymer tends to precipitate onto the surface of the solid to aid in the recovery of the filtrate in a particulate form and to prevent agglomeration during drying. The liquid mixture resulting from the prepolymerization or the inventive solid prepolymerized catalyst can be subjected to sonification to help break up particles if desired.
Further, if desired the recovered solid prepolymerized catalyst system can be screened to give particles having sizes that meet the particular needs for a particular type of polymerization.
Another option is to combine the recovered inventive solid prepolymerized catalyst system with an inert hydrocarbon, such as one of the type used as a wash liquid, and then to remove that liquid using a vacuum. In such a process it is sometimes desirable to subject the resulting mixture to sonification before stripping off the liquid.
The resulting solid prepolymerized metallocene-containing catalyst system is useful for the polymerization of olefins. Generally, it is not necessary to add any additional aluminoxane to this catalyst system. In some cases it may be found desirable to employ small amounts of an organoaluminum compound as a scavenger for poisons. The term organoaluminum compounds include compounds such as triethylaluminum, trimethylaluminum, diethylaluminum chloride, ethylaluminum dichloride, ethylaluminum sesquichloride, and the like. Trialkyl aluminum compounds are currently preferred. Also in some applications it may be desirable to employ small amounts of antistatic agents which assist in preventing the agglomeration of polymer particles during polymerization. Still further, when the inventive catalyst system is added to a reactor as a slurry in a liquid, it is sometimes desirable to add a particulate dried solid as a flow aid for the slurry. Preferably the solid has been dried using one of the methods described earlier. Inorganic oxides such as silica are particularly preferred. Currently, it is preferred to use a fumed silica such as that sold under the tradename Cab-o-sil. Generally the fumed silica is dried using heat and trimethylaluminum.
The solid catalyst system is particularly useful for the polymerization of alpha-olefins having 2 to 10 carbon atoms. Examples of such olefins include ethylene, propylene, butene-1, pentene-1,3-methylbutene-1, hexene-1,4-methylpentene-1,3-methylpentene-1, heptene-1, octene-1, decene-1,4,4-dimethyl-1-pentene, 4,4-diethyl-1-hexene, 3,4-dimethyl-1-hexene, and the like and mixtures thereof. The catalysts are also useful for preparing copolymers of ethylene and propylene and copolymers of ethylene or propylene and a higher molecular weight olefin.
The polymerizations can be carried out under a wide range of conditions depending upon the particular metallocene employed and the particular results desired. Although the inventive catalyst system is a solid, it is considered that it is useful for polymerization conducted under solution, slurry, or gas phase reaction conditions.
When the polymerizations are carried out in the presence of liquid diluents obviously it is important to use diluents which do not have an adverse effect upon the catalyst system. Typical liquid diluents include propane, butane, isobutane, pentane, hexane, heptane, octane, cyclohexane, methylcyclohexane, toluene, xylene, and the like. Typically the polymerization temperature can vary over a wide range, temperatures typically would be in a range of about xe2x88x9260xc2x0 C. to about 300xc2x0 C., more preferably in the range of about 20xc2x0 C. to about 160xc2x0 C. Typically the pressure of the polymerization would be in the range of from about 1 to about 500 atmospheres or even greater. The inventive catalyst system is particularly useful for polymerizations carried out under particle form, i.e., slurry-type polymerization conditions.
The polymers produced with this invention have a wide range of uses that will be apparent to those skilled in the art from the physical properties of the respective polymers. Applications such as molding, films, adhesives, and the like are indicated.
A further understanding of the present invention, its various aspects, objects and advantages will be provided by the following examples.